This invention relates to an improved corona discharging unit used, for example, in an electrophotographic copying machine and also an electrophotographic copying machine which incorporates such improved corona discharging unit.
As shown in FIG. 1, a corona discharging unit of conventional design used, for example, in an electrophotographic copying machine contains a corona discharge line 2 inside a grounded shield case 1 and a high voltage power source 3 is connected to this corona discharge line to effect positive, negative or AC discharge, depending upon the purpose. A screen grid 4 may be installed at the opening of the discharging unit (shield case 1) as shown in FIG. 2 so that the output can be controlled by means of a source 3 connected to the screen grid 4.
When discharges of different polarities are required, however, it is not sufficient to have a single unit of the conventional type described above. Moreover, high voltage power sources corresponding to the individual polarities (positive, negative, and AC) become necessary.
It is therefore an object of the present invention in view of the above to provide a corona discharging unit which can utilize the discharging means for charging, transferring and discharging (AC or DC) in a copying process.
It is another object of the present invention to provide an electrophotographic copying machine which eliminates the drawbacks of the conventional devices described above by unitizing a discharging unit for transferring and another unit for discharging so that a single high voltage power source can perform two functions.
It is still a further object of the present invention to provide a small, light-weight, inexpensive electrophotographic recording machine with a simplified structure by using some of the components for more than one purpose.
In order to achieve the aforementioned objectives, the corona discharging unit for use in a copying machine according to the present invention comprises a shield case, a corona discharge line installed inside this shield case, a control grid disposed in the vicinity of the opening section of the shield case for controlling the polarity and/or output of the corona discharge, a control means connected to the control grid for controlling the polarity and/or output of the corona discharge, and a high voltage AC power source connected to the aforementioned corona discharge line.
According to an embodiment of the present invention, an electrophotographic copying machine causes copy paper to contact a photosensitive means on which a toner image is formed and copying is effected by means of a corona discharging unit which comprises a single corona discharger and a single high-voltage power source. Transferring of the toner image as well as separation of the copy paper from the photosensitive means are also effected by means of this corona discharging unit.
According to another embodiment of the present invention, the electrophotographic copying machine is adapted for functions such as charging, image exposure, development, transferring, discharging and cleaning. During its operation in Mode 1, the photosensitive means is charged prior to its exposure to light and the toner image formed thereon is transferred in the Mode 2 operation. For this purpose, a corona discharging unit disposed opposite to this photosensitive means is provided with a means for selectively assigning its functions to Mode 1 and Mode 2.